The present invention is generally directed to mass analyzers. More particularly, the present invention is directed to a mass analyzer having an improved mass filter and/or ion detection arrangement.
The characteristics of mass spectrometry have raised it to an outstanding position among the various analysis methods. It has excellent sensitivity and detection limits and may be used in a wide variety of applications, e.g. atomic physics, reaction physics, reaction kinetics, geochronology, biomedicine, ion-molecule reactions, and determination of thermodynamic parameters (xcex94Gxc2x0f, Ka, etc.). Mass spectrometry technology has thus begun to progress very rapidly as its uses have become more widely recognized. This has led to the development of entirely new instruments and applications. However, development trends have gone in the direction of increasingly complex mass analyzer designs requiring highly specialized components and tight manufacturing tolerances. Additionally, significant advances toward miniaturization of mass analyzer components have not been truly realized.
One attempt to improve on existing mass analyzers is shown in U.S. Pat. No. 5,726,448, issued Mar. 10, 1998, to Smith et al. The ""448 patent purportedly describes a mass analyzer having a mass filter chamber that employs a rotating RF electric field for ion sample separation. Rotation of the electric field is achieved through the use of at least four electrodes that operate in opposed parallel pairs. A first RF signal is applied to the first pair of parallel electrodes while a second RF signal is applied to the second pair of parallel electrodes. The first and second RF signals differ in phase by xcfx80/2 and thereby generate the desired field rotation.
Two mass analyzer embodiments are identified in the ""448 patent. In the first embodiment, a mass filter chamber is used in which both the first and second electrode pairs are aligned along the same length of the mass filter chamber. In the second embodiment, the second electrode pair is displaced from the first electrode pair along the length of the mass filter chamber. In each embodiment, the electric field generated at the second electrode pair is out of phase by xcfx80/2 from the electric field generated at the first electrode pair so that the ions are acted upon by at least two distinct electric fields. Thus, at least two orthogonal electric fields are mandated for operation of each embodiment.
The ions reaching the outlet end of the mass filter chamber form a circle for each set of ions having a given mass-to-charge ratio, m/Q. It is this circular pattern that is analyzed to determine the characteristics of the sample. Accordingly, the ion detector described in the ""448 patent is configured as a two-dimensional device array that must necessarily (and without option) provide and process two coordinate values for each impinging ion. As shown in FIG. 6 of the ""448 patent, the ion detector is disposed immediately adjacent and coextensive with the ion outlet end of the mass filter chamber to ensure detection of substantially all of the ions exiting the mass filter chamber without further regard to their m/Q values.
The present inventors have recognized that existing mass spectrometer apparatus may be improved in a variety of manners. For example, decreased complexity of one or more components may be achieved by, for example, employing a single, non-rotating RF electric field in the mass filter. Alternatively, in lieu of, or in addition to the foregoing, improvements can be realized by developing unique ion detection arrangements that take advantage of predetermined ion exit angles from the mass filter of ions having selected m/Q values. Such improvements can be achieved while still maintaining or exceeding manufacturing, mass resolution, and/or mass sensitivity goals.
An improved mass analyzer is set forth. In accordance with one embodiment, the mass analyzer employs a unique mass filter design. The mass filter comprises an ion selection chamber in which sample ions are subject to an electric field for analysis. At least one pair of electrodes is disposed within the ion selection chamber. Each of the electrodes of the electrode pair may, for example, have a planar face. The electrodes may also be oriented in the ion selection chamber to place their planar faces parallel and opposite one another about a central axis. An RF signal generator is connected to the electrode pair to produce the electric field within the ion selection chamber. More particularly, the electrodes and RF signal generator cooperate to provide a non-rotating, oscillating electric field in the chamber that, ignoring any fringing effects, oscillates principally in a single coordinate plane (i.e., the y-z plane).
An ionizer/ion injector may be used to ionize sample analytes and inject such ions into the ion selection chamber. Preferably, the ion injector directs the ions toward the planar face of either or both electrodes of the electrode pair. Even more preferably, the ion injector is adapted to inject the ions at a substantial angle with respect to a further coordinate plane (i.e., the x-y plane) at the ion inlet of the ion selection chamber. Angles of at least 40xc2x0 are preferred while angles of at least 60xc2x0 are even more preferable.
In accordance with a further embodiment, the mass analyzer comprises an ionizer/ion injector, a mass filter and an ion detector. The mass filter is adapted to receive sample ions from the ionizer/ion injector and has an ion inlet and an ion outlet. The ion inlet of the mass filter is disposed proximate the ionizer/ion injector while the ion outlet constitutes an opening through which ions having a certain m/Q may pass. The ion detector is disposed proximate the ion outlet of the mass filter and is positioned to principally detect ions that exit substantially at a predetermined exit angle, xcex8e, from the ion outlet of the mass filter and to the general exclusion of ions having other exit angles.